1. Field of the Invention
The present invention relates to a prism sheet, an illuminating device, a surface emitting device, and a liquid crystal display device.
2. Description of the Related Art
Conventionally, a backlight device, which is a kind of surface emitting device, for emitting light from the rear side of a liquid crystal display panel to a display surface has been commonly used as an illuminating means of the liquid crystal display device. In general, the conventional backlight device includes a light guiding plate composed of a transparent resin plate having one edge, an emission surface orthogonal to the one edge, and a prism surface provided opposite to the emission surface; a light source arranged at the side of the one edge of the light guiding plate; a prism sheet arranged at the side of the emission surface of the light guiding plate.
In the conventional backlight device, light emitted from the light source is introduced into the light guiding plate through the one edge and is then reflected from the prism surface. Then, the reflected light is emitted from the emission surface, and the emitted light is reflected in the same direction by the prism sheet and is then emitted from the entire surface of the prism sheet. As an example of such a backlight device, a surface emitting device disclosed in Japanese Examined Patent Application Publication No. 7-27137 has been commonly known.
In the surface emitting device disclosed in the above publication, as shown in FIG. 1 of the above publication, light components emitted from a light guiding plate travel in different directions and are emitted in a dispersed state. In this publication, the dispersed light components travel in the same direction while passing through the prism sheet. However, since the prism sheet has limitations in allowing light components to travel in the same direction, it is difficult to sufficiently improve the directivity of light passing through the prism sheet.